Method of blowing metal objects into mold with porous insert



July 4, 1967 MET B. MANNING ETAL 3,329,198 HOD OF BLOWING METAL OBJECTS INTO MOLD WITH POROUS INSERT Filed Sept. 29, 1964 FIG. I

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44 MOLD AIR VENT L w SUPPLY FIG.2 r32 /46 INVENTORS BERNARD MANNING DONALD J. RICE ARION C. MANCUSO My )L y ATTORNEYS United States Patent 3,329,198 METHOD OF BLOWING METAL OBJECTS INTO MOLD WITH POROUS INeERT Bernard Manning, Waltham, and Donald J. Rice, Franklin, Mass., and Arion C. Mancuso, Valley Stream, N.Y., assignors to Ilikon Corporation, Natick, Mass., a corporation of Delaware Filed Sept. 29, 1964, Ser. No. 400,150 2 Claims. (Cl. 164-119) Our invention relates to an improved mold and a method of employing the mold to fabricate articles. In particular, our invention concerns a fluid pervious mold and a method of blowing hollow articles directly from a fused or liquid material employing the mold and of ejecting the blown article from the mold.

In the blowing of hollow metal articles as described in the present assignees copending applications Ser. No. 381,278, filed May 14, 1964 and Ser. No. 250,902, filed Jan. 11, 1963, an article is blown directly from a reservoir of liquid or molten material into the open end of a mold suspended over or immersed in the reservoir. This is accomplished by releasing a predetermined volume or charge of pressurized gas below the surface to form a bubble of material which rises and enters the open end of the mold. The bubble of material rises and expands in the mold and into intimate conformity with the inner walls of the mold cavity. The cooled or stabilized thin shell article as blown is then extracted from the mold.

In one embodiment, the orifice of a blowpipe is immersed in a molten or fused metal and a bubble of metal blown into the open end of the mold in registry with the orifice of the blowpipe. In this regard, it should be noted that the term metal is used herein in its usual metallurgical sense, and not in the sense at one time common in the glassmaking art to mean molten glass. The molten metal bubble on contacting the internal walls of the mold cavity cools and solidifies, the mold removed from the blowing position and the resultant hollow metal article removed by opening the mold or extracting the article.

In this present method an opening or means of exhaust or ventilation is required to permit the escape of the fluid entrapped in the mold above the ascending bubble of material. If this fluid is not removed rapidly enough, then in the case of molten metal bubbles, the bubble will not rise above a certain point within the mold, but solidify to form a defective article or the hubble will tend to burst during an early part of the ascent. To resolve this problem present molds are commonly provided with one or several relatively large openings or vents or other discontinuities of 0.01 inch in size or larger through which the gaseous atmosphere in the mold escapes at the desired rate during the blowing process. The vent opening is usually located at the extreme end or top of the mold away from the open end into which the bubble is blown. Vent openings also may be employed in other areas or intricate portions of the mold wherein air may tend to be entrapped by the rising bubble.

In some cases, a partial vacuum, e.g., '50 mm, of mercury is induced through an exhaust vent to remove entrapped air from the mold. The vacuum also tends to draw the bubble into the mold and thereby assist in the full formation of the desired blown article. In the formation of a 202 blown aluminum alloy container a cylindrical solid cast iron mold has been used which mold has a fitted top inset with a circumferential clearance of approximately 0.010 inch on each side to serve as a vent opening.

One problem associated with molds having air vents 3,329,198 Patented July 4, 1967 or discontinuities is the tendency of such molds to create mold areas of thermal discontinuity. Thus, the portion of the mold material about the vent openings often has a distinct temperature difierence from either the other portions of the mold such as the solid side walls or top insert of the mold. Thermal discontinuities in the mold may result in a differential cooling rate for the blown material, thermal stress and possibly cracks in the blown metal article. Another problem is that the relatively large vent openings required to permit the rapid escape of air presents no mechanical barrier to the ascending bubble, and if the blowing pressure is too high, a ridge of blown material may be created by the opening about the bottom of the hollow metal article. The vent opening or clearance space also provides an opportunity for the blown material to flow into this opening and stabilize or solidify therein. Material in the vent opening may reduce the escape of air or completely block the opening while making it extremely difficult to extract the blown articles such as by removing the fitted top insert from the mold or opening a split mold.

It is therefore an object of our invention to provide a new and improved mold which mold overcomes or reduces many of the foregoing difficulties and problems associated with solid molds having relatively large vents or discontinuities.

Another object of our invention is to provide an improved method for the rapid and automatic blowing and ejection of articles.

A further object of our invention is to provide an improved mold and method for the fabrication of hollow metal articles characterized by relatively uniform bottoms, having good stress properties and a very fine surface finish.

Other objects and advantages of our invention will be apparent to those skilled in the art from the following more detailed description of our invention taken with the accompanying drawing wherein:

FIG. 1 is a diagrammatic representation of an improved mold employed in blowing hollow metal articles; and

FIG. 2 is a diagrammatic representation of an apparatus including our improved mold illustrating a method of ejecting a blown article from the mold.

We have found that a mold fabricated from a gaspervious material of fine porosity permits blown articles having no cracks and a strong and uniform complete shell to be formed. In particular, we have discovered that molds having a sintered metal gas-pervious top insert permit blown metal articles to be formed of uniform and excellent quality. The use of sintered or porous material for the top insert or extreme portions of an open ended mold may also be used to impress a gas pressure uniformly against the bottom of the blown article after formation to eject the article from a tapered mold. Molds thus fabricated overcome many of the problems associated with solid molds having a vent opening while additionally permitting the molds to be readily employed for automatic and rapid fabrication of blown articles.

Where desired, the entire mold may be fabricated from the gas-pervious material, so that the atmosphere within the mold may be readily displaced by the: ascending bubble of material. For example, where the bubble method is subject to rapid cooling or where a very high production rate is desired, or the mold cavity is of a detailed intricate shape which tends to entrap air easily. In one preferred embodiment, the top or the extreme portions of the mold away from and opposite to the end into which the bubble is blown are fabricated from the porous material to obtain relatively uniform venting of the gas from the mold and to permit easy ejection of the blown article.

Any material may be employed which material has a fine porosity so that fiuid within the mold may be vented at the desired flow rate. The material should not appreciably be wetted by the blown material, since sticking of the blown material to the mold might occur. Porous material at the top or extreme portions of the mold tends to inhibit any sticking difficulties, since the temperature differences between the blown material and the mold is usually at a maximum and sufiicient to prevent sticking problems. In the blowing of metal or metal alloys, hard, high temperature resistant materials such as porous ceramics, or metals like stainless steel, iron, nickel, brass, bronze, low carbon steel, the noble metals, copper, titanium and the like in sintered or sponge or other porous forms may be profitably employed as the gas-pervious material. Metal materials may be formed to the proper and desired shapes for inclusion in the mold and would not require machining.

The pores of the gas-pervious material should be sufiicient in either size and number to permit the escape of the gas in the mold at the desired rate. Also, the porosity should be such as not to impair the surface finish or attractiveness or appearance of the finished blown article. The pores should not be sufficiently large enough to allow the blown material to plug up gradually these openings. Molds having fine porous material of a graded porosity may be used to control the wall thickness and surface finish of the blown article. We have found in general that an average pore diameter or size of about 0.005 of an inch or less provide an acceptable flow rate and surface finish while pores of 0.001 of an inch or less, e.g. 0.001 to 0.005 give an excellent surface finish to the blown article. The number and size of the pores are, of course, dependent upon the particular conditions of the blowing process and the finished article desired. In the blowing of hollow metal articles with a cylindrical mold having a sintered metal gas-pervious circular top insert, pores of 0.001 of an inch in size and from 5000 to 15,000 per square inch have been found satisfactory. Fabrication of all or a sub stantial portion of the mold with gas-perviou material permits graded porosity and a graded surface finish to be obtained. Such mold provides an opportunity to shape the bubble of material in the mold prior to stabilization by the use of fluid jets through the side walls of the gaspervious mold. For example, in the formation of cylindrical containers in a totally sintered metal mold, air jets may be used on the sides of the mold to blow and form gentle depressions in the hollow article prior to solidification.

The gas-pervious material may be prepared by the formation of sponge materials or by sintering materials such as powdered metals such as nickel or iron powders into the desired form. For example, a uniform gas-pervious mold material may be prepared by a series of overlaid, finely-etched screen material of increasing porosity and controlled screen size which are bonded or pressed and sintered to form a gas-pervious fine porosity solid appearing metal matrix.

FIG. 1 illustrates the formation of a hollow blown aluminum can employing a mold of our invention. In FIG. 1, a quantity of a suitable aluminum alloy, e.g. ASTM aluminum 2024 or an aluminum containing about 4 percent silicon and trace quantities of iron and other elements is contained in a reservoir vessel 12 and maintained in a molten state at a predetermined temperature of about 1260 F. by a source of heat (not shown). A blowpipe 14 having a blowpipe nozzle 16 containing a plurality of small diameter orifices 18 is immersed in the aluminum melt with the nozzle 16 disposed a predetermined distance below the melt surface. The other end of the blowpipe is connected to a source of pressurized gas (not shown) from which a regulated volume of gas may be released.

A hollow open-ended cylindrical mold 20 is suspended over the melt with its open end immersed in the melt and in registry with the blowpipe nozzle 16. In the embodiment described, the mold 20 is characterized by an internal mold cavity shaped to form a 202 tubular container such as a can. The mold has the side wall 22 formed of cast iron with the open end of the mold immersed to a depth of about 3 /2 inches into the melt. The top 24 of the mold is a circular flanged insert fabricated to a close fit of less than 0.001 of an inch clearance within the mold walls 22. The top 24 is flush with mold top and is fabricated of sintered stainless steel being a fine porosity air-pervious material having pores of the order of 0.001 inch or less and with about 10,000 pores per square inch.

A specific example employing the above apparatus was carried out employing a blowpipe nozzle 16 composed of a material not wetted by aluminum, and containing about 30 orifices of an average diameter of about 0.030 inch distributed uniformly within a %-inch center. The blowing gas was a mixture of 97 percent by volume of nitrogen and 3 percent oxygen and was released through the blowpipe at a time interval of about 0.25 second with a source pressure of approximately 25 mm. of mercury above atmosphere. A bubble of aluminum 26 was blown into the mold at a slightly increased pressure than that required when the mold contained a conventional vent opening because of the decreased flow rate of air entrapped in the mold through the sintered metal top 24. The overpressure within the mold was about 150 mm. of mercury as compared with mm. of mercury developed with the usual vent clearance of about 0.010 inch about the top of the mold. The hollow aluminum shell blown was complete, exhibited no cracks, and was strong and of uniform thickness. The aluminum did not wet or stick to the stainless steel top 24. Under comparable conditions employing the usual vent opening, the shell often exhibited cracks and was weak and not of uniform thickness.

FIG. 2 is a schematic illustration of a modified mold of FIG. 1 which may be employed both to exhaust the entrapped air and subsequently to eject the blown article. A mold 30 having solid smooth cylindrical walls 32 as a slight taper so that the diameter of the top portion is slightly smaller than the diameter of the open end into which the bubble is blown. The top of the mold body has a flange 34 and contains a fitted insert of gas-pervious material 35 with a hemispherical manifold 36 on the opposite side thereof, and secured in a fluid-tight manner to the top flange 34. A conduit 38 is connected to the one end with the manifold 36, and at the other end with a three-Way valve 40. The manifold 36 through conduit 38 is capable of being placed in communication through conduit 42 to the atmosphere as a mold vent opening or a vacuum source or through conduit 44 to a source of pressure such as an air pressurized supply or to a closed position. The valve 40 as shown is connected to conduit 44 so that pressurized air is admitted through conduit 44, valve 40, conduit 38, into the interim manifold 36 and through the porous top plug 35 and into the interior of the mold 30.

In operation, a hollow blown article 46 is formed in the mold 30 in the described manner with the valve 40 switched to conduit 42 during or just after the introduction of the bubble into the mold 30 and during the ascent of the bubble. As the bubble of material rises and contacts the internal walls of the mold cavity, the gaseous atmosphere above the melt such as air or an inert atmosphere is vented through the top plug 35 into the interior of the manifold 36 and through conduit 38, valve 40 and conduit 42. After the formation and stabilization of the article such as the solidification of the metal article, valve 40 is switched to connect conduit 44 with conduit 38 and the interior of the manifold 36. This action permits the pressurized air to enter the sintered top plug 35 I and the interior of the mold 30 and to exert a uniform force on the base of the article 46 and to eject the article from the mold. After ejection, the mold is again placed in position to receive another bubble and to repeat the blowing process with the valve 40 switched to connect conduit 42. Although the operation has been described as a manual operation, it is, of course, contemplated that the valve 40 could be a solenoid-activated single and multi-way valve responsive to the electrical or hydraulic impulses of a timer connected in any proper sequence to the steps of the fabrication process such as to the step of withdrawing the mold or introducing the blowing gas. The gas-pervious top plug 35 of the mold 30 therefore permits the mold to be used for venting purposes, and allows ejection of the blown article whereby the process of fabrication may be made automatic and rapid in operation.

Our invention provides for molds having a top plug or insert of gas-perviou material having a plurality of many fine pores. This material allows entrapped mold gas to escape and enhances the formation of strong uniform thickness blown articles of good surface finish and thermal stress properties. Also porous mold tops allow the rapid ejection in an automatic operation of the blown article from the mold by the application of a uniform gas pressure exerted against all or a substantial portion of the bottom of the article.

What we claim is:

1. A method of fabricating hollow metal articles which method comprises:

suspending the open end of a metal mold above and in registry with the orifice of one end of a blowpipe immersed a predetermined distance beneath the surface of a molten metal and o-ut of contact with the mold, the mold being characterized by an internal cavity of the desired shape of the blown article, said cavity extending from the open end of the mold to an insert at the other and opposite end of the mold of a gas-pervious fine porosity material having pores of sufficient number to exhaust entrapped gases within the mold at a desired flow rate;

introducing a predetermined volume of pressurized gas into the other end of the blowpipe to form and introduce a gas bubble of the molten metal into the open end of the mold; exhausting entrapped gases within the mold through the pores of the insert at a desired flow rate distributed smoothly over the surface of the porous insert and permitting the bubble to come into intimate contact with the entire internal cavity of the mold;

permitting the shaped bubble to solidify into the blown article; and

recovering the blown article from the mold.

2. The method of claim 1, in which the porous insert through which the entrapped gases within the mold are exhausted is made of sintered metal having pores of less than about 0.001 inch in size.

References Cited UNITED STATES PATENTS 788,142 4/1905 Pease -192 1,725,144 8/1929 Kad-ow 22-209 XR 2,209,877 7/ 1940 Ferngren 18-58 2,395,727 2/1946 Devol 65-374 XR 2,544,598 3/1951 Kalina 22-73 XR 2,584,110 2/1952 Blackburn et a1. 25-129 3,065,511 11/1962 Leitzel 22-195 3,184,296 5/1965 Schaich 65-177 3,196,501 7/1965 Balevsky et a1. 29-209 XR FOREIGN PATENTS 193,945 2/ 1923 Great Britain.

OTHER REFERENCES Websters New International Dictionary, Metal: definition 9: glass in a state of fusion.

J. SPENCER OVERHOLSER, Primary Examiner. VERNON K. RISING, Assistant Examiner. 

1. A METHOD OF FABRICATING HOLLOW METAL ARTICLES WHICH METHOD COMPRISES: SUSPENDING THE OPEN END OF A METAL MOLD ABOVE AND IN REGISTRY WITH THE ORIFICE OF ONE END OF A BLOWPIPE IMMERSED A PREDETERMINED DISTANCE BENEATH THE SURFACE OF A MOLTEN METAL AND OUT OF CONTACT WITH THE MOLD, THE MOLD BEING CHARACTERIZED BY AN INTERNAL CAVITY OF THE DESIRED SHAPE OF THE BLOWN ARTICLE, SAID CAVITY EXTENDING FROM THE OPEN END OF THE MOLD TO AN INSERT AT THE OTHER AND OPPOSITE END OF THE MOLD OF A GAS-PERVIOUS FINE POROSITY MATERIAL HAVING PORES OF SUFFICIENT NUMBER TO EXHAUST ENTRAPPED GASES WITHIN THE MOLD AT A DESIRED FLOW RATE; INTRODUCING A PREDETERMINED VOLUME OF PRESSURIZED GAS INTO THE OTHER END OF THE BLOWPIPE TO FORM AND INTRODUCE A GAS BUBBLE OF THE MOLTEN METAL INTO THE OPEN END OF THE MOLD; EXHAUSTING ENTRAPPED GASES WITHIN THE MOLD THROUGH THE PORES OF THE INSERT AT A DESIRED FLOW RATE DISTRIBUTED SMOOTHLY OVER THE SURFACE OF THE POROUS INSERT AND PERMITTING THE BUBBLE TO COME INTO INTIMATE CONTACT WITH THE ENTIRE INTERNAL CAVITY OF THE MOLD; PERMITTING THE SHAPED BUBBLE TO SOLIDIFY INTO THE BLOWN ARTICLE; AND RECOVERING THE BLOWN ARTICLE FROM THE MOLD. 